Lensless zoom hologram system paves the way for small, low-cost portable projectors
October 17, 2013
Imagine giving an important presentation when suddenly the projector fails. You whip out your smartphone, beam your PowerPoint presentation onto the conference-room screen, and are back in business within seconds.
When fully developed, the system should be cheaper and smaller than other projection systems, which typically require expensive, complicated lenses and mechanical components, the researchers report in a paper just published in the Optical Society’s (OSA) journal Optics Express (open access).
The new holographic lensless zoom is not the first lensless zoom system to be developed, but Tomoyoshi Shimobaba, a professor in the graduate school of engineering at Chiba University in Japan, notes that his team’s system requires only a laser and an LCD panel.
Holograms replace lenses
To achieve a lensless zoom, Shimobaba, his colleagues from Chiba University, and Michal Makowski from the Warsaw University of Technology in Poland turned to holography.
Holography is a way to produce images by using the interference pattern of two laser beams to encode and later display the image. By their nature holograms operate without lenses. It is possible to represent a holographic image with numbers and formulas and then calculate how that image can be magnified.
Shimobaba and his team made modifications to the standard magnification formulas to reduce calculation time and preserve image quality. Magnified holograms can suffer from a signal processing effect called aliasing, which can result in visual distortions of the original image.
The researchers developed a calculation to reduce aliasing effects and also used a method developed by another team of researchers to reduce the speckle noise effect that can give holograms a grainy appearance.
They tested the technique by increasing by nine times the size of the standard test image of a woman in a feathered hat.
Currently the footprint of the holographic zoom system is about 16x8x4 centimeters, but Shimobaba believes the researchers can easily shrink it even further.
He estimates that the technology could be commercialized in the next five to ten years.
The researchers next plan to refine their mathematical image manipulation techniques to further improve image quality and reduce calculation time. They also plan to test the technique with color images.
Abstract of Optics Express paper
Projectors require a zoom function. This function is generally realized using a zoom lens module composed of many lenses and mechanical parts; however, using a zoom lens module increases the system size and cost, and requires manual operation of the module. Holographic projection is an attractive technique because it inherently requires no lenses, reconstructs images with high contrast and reconstructs color images with one spatial light modulator. In this paper, we demonstrate a lensless zoomable holographic projection. Without using a zoom lens module, this holographic projection realizes the zoom function using a numerical method, called scaled Fresnel diffraction which can calculate diffraction at different sampling rates on a projected image and hologram.
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